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Crystal structure of a homotrimeric verrucomicrobial exo-β-1,4-mannosidase active in the hindgut of the wood-feeding termite Reticulitermes flavipes

DOI: 10.1016/j.yjsbx.2021.100048 DOI Help

Authors: Dayanand C. Kalyani (KTH Royal Institute of Technology) , Tom Reichenbach (KTH Royal Institute of Technology) , Markus M. Keskitalo (KTH Royal Institute of Technology) , Julian Conrad (Stockholm University) , Henrik Aspeborg (KTH Royal Institute of Technology) , Christina Divne (KTH Royal Institute of Technology)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of Structural Biology: X , VOL 22

State: Published (Approved)
Published: May 2021
Diamond Proposal Number(s): 15806

Open Access Open Access

Abstract: The termite Reticulitermes flavipes causes extensive damage due to the high efficiency and broad specificity of the ligno- and hemicellulolytic enzyme systems produced by its symbionts. Thus, the R. flavipes gut microbiome is expected to constitute an excellent source of enzymes that can be used for the degradation and valorization of plant biomass. The symbiont Opitutaceae bacterium strain TAV5 belongs to the phylum Verrucomicrobia and thrives in the hindgut of R. flavipes. The sequence of the gene with the locus tag opit5_10225 in the Opitutaceae bacterium strain TAV5 genome has been classified as a member of glycoside hydrolase family 5 (GH5), and provisionally annotated as an endo-β-mannanase. We characterized biochemically and structurally the opit5_10225 gene product, and show that the enzyme, Op5Man5, is an exo-β-1,4-mannosidase [EC] that is highly specific for β-1,4-mannosidic bonds in mannooligosaccharides and ivory nut mannan. The structure of Op5Man5 was phased using electron cryo-microscopy and further determined and refined at 2.2 Å resolution using X-ray crystallography. Op5Man5 features a 200-kDa large homotrimer composed of three modular monomers. Despite insignificant sequence similarity, the structure of the monomer, and homotrimeric assembly are similar to that of the GH42-family β-galactosidases and the GH164-family exo-β-1,4-mannosidase Bs164 from Bacteroides salyersiae. To the best of our knowledge Op5Man5 is the first structure of a glycoside hydrolase from a bacterial symbiont isolated from the R. flavipes digestive tract, as well as the first example of a GH5 glycoside hydrolase with a GH42 β-galactosidase-type homotrimeric structure.

Journal Keywords: exo-β-14-mannosidase; glycosyl hydrolase family 5; termite hindgut; crystal structure; electron cryo-microscopy; Reticulitermes flavipes; Verrucomicrobia; Opitutaceae

Diamond Keywords: Bacteria; Enzymes

Subject Areas: Biology and Bio-materials, Chemistry

Instruments: I03-Macromolecular Crystallography

Other Facilities: Cryo-EM Swedish National Facility

Added On: 25/05/2021 15:43


Discipline Tags:

Biochemistry Catalysis Chemistry Structural biology Life Sciences & Biotech

Technical Tags:

Diffraction Macromolecular Crystallography (MX)